Rotary machines, for example turbo or compressor stages of gas or steam turbine plants, for the specific expansion or compression of gases or gas mixtures, generally have fixed guide blades and moving blades rotating about a rotation axis. The blades can be exposed to high process temperatures and therefore may have to withstand high thermal loads. In addition to the thermal load, the moving blades in particular, rotating about the rotation axis, may additionally be subjected to high mechanical loads caused by the centrifugal forces.
In the attempt to improve the efficiency of such heat engines, measures can be taken which result in the rotating components being subjected to ever increasing thermal and mechanical loads on account of increasing process temperatures and increased rotary speeds. However, these attempts can be subject to physical load limits on account of the materials used, from which in particular the rotating plant components can be produced. To optimize the efficiency even further, ways of effectively cooling the plant components exposed to heat and subjected to centrifugal force are looked for. To this end, a number of proposals with which cooling air is admitted to moving blades in rotary machines are already known. Typically, a moving blade of such a design, in order to fasten it to the rotor, has a moving blade root which is structured like a fir tree stem, and the moving blade airfoil radially adjoins this moving blade root. For cooling purposes, a multiplicity of radially oriented cooling passages can pass through the moving blade root, these cooling passages, for the effective cooling of the moving blade, extending along the inner walls through the entire moving blade airfoil. Cooling-air feed passages provided on the rotor serve to feed cooling air, which is fed into the cooling passages passing radially through the moving blade root. Such a cooling-air supply system therefore includes a rotor which has a multiplicity of radially oriented cooling-air passages and whose individual cooling passages, by appropriate positioning of the individual moving blades, can be brought exactly into alignment with the radial cooling passages provided in the moving blade root. Even the slightest maladjustments between moving blade root and rotor unit may permanently impair effective cooling of the moving blade, thereby considerably reducing the service life of the moving blade.
As an alternative to radially supplying a moving blade with cooling air via a rotor-side cooling-air supply system, it has been proposed to effect the cooling-air supply via a cooling-air supply passage passed axially through the moving blade root. In this case, the cooling-air feed flow passes into the axially oriented cooling-air supply passage inside the moving blade root, branching off from which are individual cooling-air passages projecting radially into the moving blade root. Since moving blades are generally produced by a casting process, the “core technique” is used for forming such cavities inside a cast part, this core technique in particular enabling the cooling-air supply passage passing axially through the moving blade root and the individual cooling passages passing radially at least partly through the inside of the moving blade airfoil to be produced. However, it has been found that flow baffles have to be provided inside the axially oriented cooling-air supply passage for optimized distribution of the cooling-air feed flow, these flow baffles being intended to deflect the axially directed cooling-air feed flow into the radially extending cooling passages inside the moving blade root. However, for production reasons, the flow baffles which are to be provided for this purpose and which both change the direction of and distribute the cooling-air feed flow axially directed into the blade root can be subject to production-related structural shape tolerances, which reduce the accuracy with which the cooling-air flow can be directed and distributed to the individual cooling passages extending radially along the moving blade airfoil.